Protesters run from security forces and tear gas and into Tahrir Square.
It's the fourth day of clashes in Cairo since protests marking Egypt's 2011 revolution began Thursday evening.
Dozens have died and hundreds have been wounded nationwide.
Stone-throwing, volleys of noxious gas and even live fire have become familiar over two years of sporadic unrest.
The latest violence and mounting death toll are challenging President Mohamed Mursi and his Islamist allies - whom opponents accuse of betraying the uprising that overthrew Hosni Mubarak.
Military forces also deployed in the northern city of Port Said Sunday following the deaths of at least 30 people in clashes with police.
Residents were protesting a court verdict that sentenced 21 people, most from the coastal city, to death over a football riot last year.
There have also been reports of gunshots amid a funeral procession for the victims of yesterday's protests.
